If you're looking for fitness motivation, GymPact lets you make a deal with other users. If you live up to your goal, you make money. If you don’t, you pay. Also, with Fooducate you scan items at the grocery store and it will tell you just how healthy they are.

Almost all of these are good for iPhones and Androids, but some are only good for iPhones.

The American Heart Association's Pocket First Aid and CPR and the American Academy of Pediatrics' KidsDoc cost $1.99, but all the rest are free.